The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System in use today. It employs a constellation of at least 24 satellites in Medium Earth Orbit that transmit microwave frequency transmissions, the system enables a GPS receiver to calculate its global location, velocity, direction, and time. There are similar systems such as the Russian built GLONASS still under development as well as the long awaited European Galileo system for global positioning, the proposed COMPASS navigation system from China, and the IRNSS of India.

The GPS System was Developed by the United States Department of Defense, and it is officially named the NAVSTAR GPS. NAVSTAR is not an acronym, but simply a name given by Mr. John Walsh, a key decision maker when it came to the budget for the network

The satellites are managed by the United States Air Force 50th Space Wing. The total estimated cost of maintaining the system is approximately US$750 million per year, including the replacement of obsolete satellites, as well as R&D.

Following the shooting down of Korean Air Lines Flight 007 in 1983, President Reagan issued a directive making the system available free for civilian use. Since then, GPS has become a widely used aid to navigation worldwide, and a useful tool for map-making, land surveying, commerce, and scientific uses as well as recreational uses such as bushwalking, hiking, camping, caravaning, orienteering, and of course in vehicle street navigation. GPS also provides a precise time reference used in many applications including scientific study of earthquakes, and synchronization of telecommunications networks since each satellite in the constellation houses an atomic clock.